A micro-to-macroscale and multi-method investigation of human sweating dynamics

Area of Science:

• Biophysics
• Human Physiology
• Thermal Regulation

Background:

• Human thermoregulation and comfort in hot environments depend on sweat secretion and evaporation.
• Previous studies primarily used macroscopic methods, leaving micro-to-macroscale sweating dynamics poorly understood.

Purpose of the Study:

• To explore the unexplored micro-to-macroscale dynamics of human sweating.
• To investigate sweating onset and different sweating modes using a multi-modal approach.

Main Methods:

• Coupled micro-imaging (visible light, midwave infrared, optical coherence tomography) and macroscale physiological measurements (sweat rate, skin conductance, epidermis hydration).
• Utilized an 'air jet' capsule for sweat rate measurement, inspired by industrial jet cooling.
• Studied forehead sweating dynamics in six subjects during passive heating and cooling cycles.

Main Results:

• Relative dynamics of physiological measurements align with prior observations and are explained by imaged microscale sweating dynamics.
• Identified distinct sweating modes: porewise, transition, and filmwise.
• Highlighted the influence of stratum corneum hydration, salt deposits, and microscale hair on sweating.

Conclusions:

• Provides novel insights into the biophysical dynamics of sweating onset and progression.
• Demonstrates the utility of combined micro-imaging and physiological measurements for studying sweating.
• Offers a foundation for understanding skin interactions with cosmetics, textiles, and wearable sensors.